1. Field of the Invention
This invention relates to the field of hybrid microelectronic technology and more specifically to a leadform configuration and system for mounting so called "surface mount" components on a variety of substrates in such a manner which provides solder connections which are more resistant to thermal stresses which occur in the manufacturing and operating environment of the hybrid structure.
Reference is made to U.S. patent application No. 614,366 "Mounting System for Stress Relief in Surface Mounted Components" filed on behalf of Dennis J. Derfiny et al. on May 29, 1984 and assigned to the assignee of the present invention.
2. Description of the Prior Art
Hybrid and printed circuit technologies have existed for many years, however the trend in the electronics industry is toward smaller components which are necessarily less able to resist failures which occur due to a variety of stresses. The use of leadless chip and surface mounted (So-Type packages) components in electrical and electronics assemblies has led to new problems in the way assemblies are manufactured. Depending on the type and size of components used, for example resistors, capacitors, or transistiors, the effects of circuit media type, component bonding methods, media deflection, and environmental thermal characteristics may combine to cause component degradation and eventual failure. An example of this effect is the use of ceramic leadless components on epoxy fiberglass type media. These materials exhibit a large difference in the coefficient of thermal expansion and it takes relatively few thermal excursions to weaken the component connection to the circuitry, inducing fractures and eventually failures. Component degradation of this type has been well documented and represents a growing problem with respect to circuit quality and product reliability. Thermal gradients occur during circuit soldering, bonding, or during circuit operation.
One method which has been used to counter thermal stress is to use special mixes of solder which maintain their malleability longer than conventional solder compounds. These alternatives solder compound may present special problems with handling and manufacturing as well as being typically priced five to ten times the price of standard solder compounds.
Another method for reducing stress in surface mounted leadless components is to provide end terminations on leadless components which are constructed of either silver or palladium silver. These compounds pose special problems with solder contamination and may only temporarily delay component failure.